Switchable FMCW/PMCW Radar Transceiver

ABSTRACT

Automotive radar methods and systems for enhancing resistance to interference using a built-in self-test (BIST) module. In one illustrative embodiment, an automotive radar transceiver includes: a signal generator that generates a transmit signal; a modulator that derives a modulated signal from the transmit signal using at least one of phase and amplitude modulation; at least one receiver that mixes the transmit signal with a receive signal to produce a down-converted signal, the receive signal including the modulated signal during a built-in self-test (BIST) mode of operation; and at least one transmitter that drives a radar antenna with a selectable one of the transmit signal and the modulated signal.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication No. 62/839,927, filed on Apr. 29 2019, the entire contentsof which is incorporated herein by reference.

BACKGROUND

In the quest for ever-safer and more convenient transportation options,many car manufacturers are developing self-driving cars which require animpressive number and variety of sensors, often including arrays ofacoustic and/or electromagnetic sensors to monitor the distance betweenthe car and any nearby persons, pets, vehicles, or obstacles. As thenumbers of vehicles employing such sensors increases, so too does thepotential for these vehicles to cause interference with each other'smeasurements. Existing sensor systems fail to adequately address therisks of such interference.

SUMMARY

Accordingly, there are disclosed herein automotive radar methods andsystems for enhancing resistance to interference using a built-inself-test (BIST) module. In one illustrative embodiment, an automotiveradar transceiver includes: a signal generator that generates a transmitsignal; at least one modulator that derives a modulated signal from thetransmit signal using at least one of phase and amplitude modulation; atleast one receiver that mixes the transmit signal with a receive signalto produce a down-converted signal, the receive signal including themodulated signal during a built-in self-test (BIST) mode of operation;and at least one transmitter that drives a radar antenna with either theoriginal transmit signal or the modulated transmit signal.

In an illustrative embodiment of a method for manufacturing a radartransceiver, the method includes: providing a signal generator togenerate a transmit signal; coupling the transmit signal to a modulatorto derive a modulated signal using at least one of phase and amplitudemodulation; coupling the transmit signal to a mixer in a receiver todown-convert a receive signal; implementing a built-in self-test (BIST)mode of operation by selectably injecting the modulated signal into thereceive signal; and providing transmission flexibility with a switchthat selectably couples one of the transmit signal and the modulatedsignal to a transmitter.

In an illustrative embodiment of a method for operating a radartransceiver, the method includes: generating a transmit signal, thetransmit signal being coupled to a mixer in a receiver to down-convert areceive signal; modulating the transmit signal using phase modulation toproduce a modulated signal; injecting the modulated signal into thereceive signal during a built-in self-test (BIST); verifying operationof the receiver during the built-in self-test; and selecting a frequencymodulation or phase modulation transmission mode.

Each of the foregoing embodiments may be employed individually orconjointly, and they may further employ one or more of the followingoptional features in any suitable combination: 1. the down-convertedsignal is coupled to a measurement controller that derives a reflectordistance and velocity from the down-converted signal. 2. the measurementcontroller provides a digital baseband signal that the modulator appliesto the transmit signal using said at least one of phase and amplitudemodulation. 3. the modulator is a phase modulator. 4. the signalgenerator frequency modulates the transmit signal to provide a chirpwaveform. 5. the frequency modulation is selectably disabled duringtransmission of the modulated signal. 6. the receiver is one of multiplereceivers that each mix the transmit signal with a respective receivesignal to produce a respective down-converted signal. 7. the transmitteris one of multiple transmitters that each drive a respective radarantenna with a respective copy of the transmit signal or the modulatedsignal. 8. The transmitter is one of multiple transmitters where eachincludes a separate modulator. 9. coupling a digital baseband signalfrom the measurement controller to the modulator to modulate thetransmit signal. 10. said selecting includes: transmitting the transmitsignal, the transmit signal including a chirp waveform; processing thedown-converted receive signal to determine a distance to a reflector andrelative velocity; if the down-converted receive signal is indicative ofinterference, selecting the phase modulation transmission mode; and ifthe down-converted receive signal is not indicative of interference,selecting the frequency modulation transmission mode. 11. transmittingthe transmit signal in the frequency modulation transmission mode, thetransmit signal including a chirp waveform. 12. transmitting themodulated signal in the phase modulation transmission mode.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an overhead view of an illustrative vehicle equipped withsensors.

FIG. 2 is a block diagram of an illustrative driver-assistance system.

FIG. 3 is a schematic of an illustrative reconfigurable MIMO radarsystem.

FIG. 4A is a block diagram of a first illustrative MIMO radartransceiver.

FIG. 4B is a block diagram of an illustrative MIMO radar transceiverwith a respective modulator for each transmitter.

FIG. 5 is a flow diagram of an illustrative radar transceiver operationmethod.

DETAILED DESCRIPTION

It should be understood that the accompanying drawings and followingdetailed description do not limit the disclosure, but on the contrary,they provide the foundation for understanding all modifications,equivalents, and alternatives falling within the scope of the appendedclaims. Specific configurations, parameter values, and operationexamples are provided for the purposes of explanation rather than forcircumscribing any scope of disclosure.

FIG. 1 shows an illustrative vehicle 102 equipped with a set ofultrasonic parking-assist sensors 104 and a multiple-inputmultiple-output (MIMO) radar antenna array 106. The type, number, andconfiguration of sensors in the sensor arrangement for vehicles havingdriver-assist and self-driving features varies. For example, at leastsome contemplated MIMO radar arrays for autonomous vehicles include fourtransmit antennas and eight or more receive antennas arranged to scanahead of, around, and behind the vehicle. The vehicle may employ thesensor arrangement for detecting and measuring distances/directions toobjects in the various detection zones to enable the vehicle to navigatewhile avoiding other vehicles and obstacles.

FIG. 2 shows an electronic control unit (ECU) 202 coupled to the variousultrasonic sensors 204 and a radar array controller 205 as the center ofa star topology. Of course, other topologies including serial, parallel,and hierarchical (tree) topologies, are also suitable and contemplatedfor use in accordance with the principles disclosed herein. The radararray controller 205 couples to the transmit and receive antennas in theradar antenna array 106 to transmit electromagnetic waves, receivereflections, and determine a spatial relationship of the vehicle to itssurroundings. To provide automated parking assistance, the ECU 202 mayfurther connect to a set of actuators such as a turn-signal actuator208, a steering actuator 210, a braking actuator 212, and throttleactuator 214. ECU 202 may further couple to a user-interactive interface216 to accept user input and provide a display of the variousmeasurements and system status.

Using the interface, sensors, and actuators, ECU 202 may provideautomated parking, assisted parking, lane-change assistance, obstacleand blind-spot detection, autonomous driving, and other desirablefeatures. In an automobile, the various sensor measurements are acquiredby one or more electronic control units (ECU), and may be used by theECU to determine the automobile's status. The ECU may further act on thestatus and incoming information to actuate various signaling and controltransducers to adjust and maintain the automobile's operation. Among theoperations that may be provided by the ECU are various driver-assistfeatures including automatic parking, lane following, automatic braking,and self-driving.

To gather the necessary measurements, the ECU may employ a MIMO radarsystem. Radar systems operate by emitting electromagnetic waves whichtravel outward from the transmit antenna before being reflected back toa receive antenna. The reflector can be any moderately reflective objectin the path of the emitted electromagnetic waves. By measuring thetravel time of the electromagnetic waves from the transmit antenna tothe reflector and back to the receive antenna, the radar system candetermine the distance to the reflector and its velocity relative to thevehicle. If multiple transmit or receive antennas are used, or ifmultiple measurements are made at different positions, the radar systemcan determine the direction to the reflector and hence track thelocation of the reflector relative to the vehicle. With moresophisticated processing, multiple reflectors can be tracked. At leastsome radar systems employ array processing to “scan” a directional beamof electromagnetic waves and construct an image of the vehicle'ssurroundings. Both pulsed and continuous-wave implementations of radarsystems can be implemented.

FIG. 3 shows an illustrative system having a MIMO configuration, inwhich J transmitters are collectively coupled to M transmit antennas tosend transmit signals. The M possible signals may variously reflect fromone or more targets to be received via N receive antennas coupled to Preceivers. Each receiver may extract the amplitude and phase or traveldelay associated with each of the M transmit signals, thereby enablingthe system to obtain N*M measurements (though only J*P of themeasurements may be obtained concurrently). The processing requirementsassociated with each receiver extracting J measurements can be reducedvia the use of time division multiplexing and/or orthogonal coding. Theavailable antennas are systematically multiplexed to the availabletransmitters and receivers to collect the full set of measurements forradar imaging.

FIG. 4A shows an illustrative radar transceiver 402 which may beimplemented as an integrated circuit in a packaged chip. The illustratedtransceiver 402 includes four transmitters TX-1 through TX-4, eachconnected to a respective transmit antenna in transmit antenna array301. The illustrated transceiver 402 further includes four receiversRX-1 through RX-4, each connected to two receive antennas in receiveantenna array 302. Each receiver includes low noise amplifiers (LNAs) toamplify the signal from the antenna, a switch to select between theantenna signals (and a test signal), and a mixer to downconvert theselected signal to baseband. Alternative embodiments may further includeintermediate frequency (IF) buffers, filters, amplifiers, etc., as wellas mixer-first receivers, in accordance with known receiver designs.

A measurement controller 404 receives the downconverted signals from thereceivers and processes them to derive measurements such as distance tothe signal reflectors, direction of the reflectors, and relativevelocity of the reflectors. The controller 404 may store themeasurements in internal registers and communicate the measurements viaa communications bus to the ECU. In at least some contemplatedembodiments, the controller 404 is a digital signal processor (DSP) chipexternal to the transceiver 402, but some embodiments may integrate thecontroller onto the transceiver chip.

The controller 404 further supplies parameter values (e.g., frequencyband, chirp rate) to a carrier signal generator 406 to control thetransmitted radar waveform. The choice of the radar waveform has asignificant impact on parameters such as range and velocity resolution,spectral efficiency, and sensitivity to interference.Frequency-Modulated Continuous Wave (FMCW) signals employ chirpwaveforms (i.e., frequency-sweeps) to increase bandwidth and therebyachieve high range resolution. However, other waveforms such asPhase-Modulated Continuous-wave (PMCW) signals, can provide true MIMOwithout time division, and are less likely to sense interference fromother radars, particularly when the source of the interference is anFMCW waveform.

Signal generator 406 includes a chirp generator to create an FMCWsignal.

The chip rate may be controlled and optionally disabled to provide anunmodulated carrier signal. The signal generator may be implemented,e.g., as a fractional-N phase lock loop (PLL) with a ΣΔ controller, oras a direct-digital synthesis (DDS) PLL. A signal splitter 408 splitsthe signal from generator 406, sending one copy to a 1:N splitter 410for distribution to the receivers RX-1 through RX-4 for use indownconversion. The other copy is coupled to a switch S1 that couplesthe signal to a modulator 412 or a modulator bypass line. The output ofmodulator 412 is coupled by a second switch S2 to either a 1:N splitter416 (which distributes the modulated signal to the receivers as a testsignal) or to a third switch S3.

Switch S3 selects either the bypass line (carrying the FMCW signal fromgenerator 406) or the modulator output line (carrying a modulated signalfrom modulator 412) as input for a 1:N splitter 414, which distributesthe selected signal to the transmitters TX-1 through TX-4 fortransmission. (Note that N represents arbitrary positive integer whichmay be different value for the transmitters than the receivers.) Thetransmitters include power amplifiers for driving the associatedantennas. Each transmitter may be selectively enabled or disabled, andthe enabled transmitters may provide a phase shift to provide thetransmit antenna array with beam-forming and/or beam-steeringfunctionality.

The switches S1-S3 may be implemented as standard single-poledouble-throw (SPDT) switches, or with split-steer amplifiers andcombine-steer amplifiers as disclosed in copending application No.62/830,083, titled “Amplifiers suitable for mm-wave signal splitting andcombining” and filed May 4, 2019 (ONS03111). The split-steer amplifiersmay also be used in place of the splitters to enable gracefuldegradation and to provide gain.

Modulator 412 provides amplitude and/or phase modulation of the signalfrom generator 406 to produce a modulated signal. The modulator may beimplemented as a quadrature (I/O) modulator, bi-phase (BPSK) modulator,or an on-off keying (00K) modulator. It can also be based on a phaseshifter with sufficient state-switching speed. The modulated signal canbe routed to the receivers as a test signal to verify that the receivechain components are operating correctly or to detect malfunctions. Thistest signal enables the transceiver to comply with safety standards thatrequire frequent self-testing. In at least some contemplatedembodiments, the built-in self-testing (BIST) of the receivers isperformed by modulating a fraction of the generated transmit signalusing a phase modulator and injecting it to the receiver input. Thedown-converted signal is then compared to the modulating signal todetect errors in the receive chain.

In the illustrated transceiver embodiment, the phase modulator 412 isused for both BIST and for generation of PMCW signals. The transceivercan operate in three modes: FMCW mode, CW mode, and BIST mode. In FMCWmode, the generator 406 generates an FMCW transmit signal having a chirpwaveform. The switches are set to route the FMCW signal to thetransmitters via the modulator bypass path, and the receivers use theFMCW signal for downconversion.

In the CW mode, frequency modulation is disabled so that the generator406 generates an unmodulated carrier signal. The switches are set toroute the carrier signal to the modulator and the modulated signal fromthe modulator to the transmitters. The modulator 412 accepts a digitalbaseband signal from the controller 404 to specify the phase modulationfor the modulated signal. The receivers use the unmodulated carriersignal for downconversion.

In the BIST mode, the controller 404 sets the generator to provideeither a carrier or a chirped signal which is routed to the receiversfor downconversion. The switches are set to route the signal from thegenerator to the modulator and from the modulator to the input of thereceivers. The illustrated embodiment shows the use of a switch toinject the test signal to the receiver input, but alternativeembodiments employ directional couplers, coupling inductors, and/orcapacitive or resistive impedance dividers. The modulator 412 accepts adigital baseband signal from the controller 404 to specify the phasemodulation for the modulated signal.

The illustrated embodiment thus enables the radar to transmit eitherFMCW or PMCW signals at a minimum added cost of silicon area andcomplexity. Potential advantages include: better waveform designflexibility, and reduced sensitivity to interference. Mutualinterference between automotive radar sensors is a significant obstacleto full-scale deployment of the technology. However, with the ability tospecify new phase-modulated waveform designs, system designers candevelop coded signals that provide orthogonality and interferenceimmunity. An external DSP module (such as controller 404) can employ thebaseband signal input to modulator 412 to add interference resilience tothe illustrated transceiver.

The principles set forth above can be extended to a transceiver havingseparately-modulated transmit signals. FIG. 4B shows an illustrativeembodiment in which the carrier/chirp generator 406 provides the carriersignal via the 1:2 splitter 408 to 1:N splitters 410 and 414. Splitter414 supplies copies of the carrier signal to each of N modulators 412,one for each of the transmitters TX-1 thru TX-4. The modulators may beseparately controlled by the measurement controller, enablingsimultaneous transmission of multiple signals with differentmodulations. A switch S2 in each transmitter enables the modulatoroutput to be directed to either the respective transmit antenna or to anN:1 combiner 417. Combiner 417 supplies a combined signal to splitter416, which operates as described previous to provide a BIST signal tothe set of receiver RX-1 thru RX-4.

FIG. 5 is a flow diagram of an illustrative radar transceiver operationmethod. In block 502, the controller places the transceiver in BIST modeto verify operation of the transceiver components, including testing thereceivers by injecting a modulated test signal at the receiver inputs.In block 504, the controller disables any transmitters or receivers thathave been determined to be malfunctioning. In block 506, the controlleruses the remaining transmitters and receivers to acquire measurements,using either the FMCW or the PMCW measurement mode. The controllerprocesses the downconverted signals to determine distance, direction,and velocity of reflectors in the region of interest. In block 508, thecontroller determines whether any interference is detected during themeasurement acquisition and, if so, switches from the FMCW mode to thePMCW mode or from PMCW mode to FMCW mode for subsequent measurements. Ifno interference is detected, the current mode is maintained. Thecontroller repeats blocks 502-508 to acquire the subsequentmeasurements.

Though the operations described herein may be set forth sequentially forexplanatory purposes, in practice the method may be carried out bymultiple components operating concurrently and perhaps evenspeculatively to enable out-of-order operations. The sequentialdiscussion is not meant to be limiting. Moreover, the focus of theforegoing discussions has been radar sensors, but the principles areapplicable to any pulse-echo or continuous-wave travel time measurementsystems. These and numerous other modifications, equivalents, andalternatives, will become apparent to those skilled in the art once theabove disclosure is fully appreciated. It is intended that the followingclaims be interpreted to embrace all such modifications, equivalents,and alternatives where applicable.

1. A transceiver comprising a signal generator configured to generate atransmit signal; a modulator configured to derive a modulated signalfrom the transmit signal using phase modulation; at least one receiverconfigured to mix the transmit signal with a receive signal to produce adown-converted receive signal, the receive signal comprising themodulated signal during a built-in self-test (BIST) mode of operation;verifying operation of the receiver during the BIST mode of operation;and selecting a frequency modulation or phase modulation transmissionmode, wherein the selecting comprises: transmitting the transmit signal,the transmit signal comprising a chirp waveform; processing thedown-converted receive signal to determine a distance to a reflector;when the down-converted receive signal is indicative of interference,selecting the phase modulation transmission mode; and when thedown-converted receive signal is not indicative of interference,selecting the frequency modulation transmission mode.
 2. The transceiverof claim 1, wherein the down-converted receive signal is coupled to ameasurement controller configured to derive the reflector distance fromthe down-converted receive signal.
 3. The transceiver of claim 2,wherein the measurement controller is further configured to provide adigital baseband signal that the modulator is configured to apply to thetransmit signal using the at least one of phase modulation.
 4. Thetransceiver of claim 3, wherein the modulator is a phase modulator. 5.The transceiver of claim 1, wherein the signal generator frequency isconfigured to modulate the transmit signal to provide the chirpwaveform.
 6. The transceiver of claim 5, wherein the frequencymodulation is configured to be selectably disabled during transmissionof the modulated signal.
 7. The transceiver of claim 1, wherein the atleast one receiver is one of multiple receivers that each are configuredto mix the transmit signal with a respective receive signal to produce arespective down-converted receive signal.
 8. The transceiver of claim 1,wherein the at least one transmitter is one of multiple transmittersthat each are configured to drive a respective radar antenna with arespective copy of the transmit signal or the modulated signal.
 9. Thetransceiver of claim 1, wherein the at least one transmitter is one ofmultiple transmitters each have a separate modulator configured toderive a respective modulated signal for each of multiple radarantennas.
 10. A method of operating a radar transceive, comprising:providing a signal generator to generate a transmit signal; coupling thetransmit signal to a modulator to derive a modulated signal using phasemodulation; coupling the transmit signal to a mixer in a receiver todown-convert a receive signal; implementing a built-in self-test (BIST)mode of operation by selectably injecting the modulated signal into thereceive signal; verifying operation of the receiver during the BIST modeof operation; and providing transmission flexibility with a switch thatselectably couples one of the transmit signal and the modulated signalto a transmitter based on a selected frequency modulation or phasemodulation transmission mode, wherein selecting the frequency modulationor phase modulation transmission mode comprises: transmitting thetransmit signal, the transmit signal comprising a chirp waveform;processing the down-converted receive signal to determine a distance toa reflector; when the down-converted receive signal is indicative ofinterference, selecting the phase modulation transmission mode; and whenthe down-converted receive signal is not indicative of interference,selecting the frequency modulation transmission mode.
 11. The method ofclaim 10, further comprising: coupling the down-converted receive signalto a measurement controller that derives the reflector distance from thedown-converted receive signal.
 12. The method of claim 11, furthercomprising: coupling a digital baseband signal from the measurementcontroller to the modulator to modulate the transmit signal.
 13. Themethod of claim 10, wherein the modulator is a phase modulator.
 14. Themethod of claim 10, wherein the signal generator frequency modulates thetransmit signal to provide the chirp waveform.
 15. The method of claim14, wherein the frequency modulation is selectably disabled duringtransmission of the modulated signal.
 16. The method of claim 10,wherein the receiver is one of multiple receivers that each mix thetransmit signal with a respective receive signal to produce a respectivedown-converted receive signal.
 17. The method of claim 10, wherein thetransmitter is one of multiple transmitters that each drive a respectiveradar antenna with a respective copy of the transmit signal or themodulated signal.
 18. The transceiver of claim 1, wherein thetransceiver is configured to transmit the transmit signal in thefrequency modulation transmission mode, the transmit signal comprisingthe chirp waveform.
 19. The transceiver of claim 1, wherein thetransceiver is configured to transmit the modulated signal in the phasemodulation transmission mode.
 20. The method of claim 10, wherein themethod comprises transmitting the transmit signal in the frequencymodulation transmission mode, the transmit signal comprising the chirpwaveform, or transmitting the modulated signal in the phase modulationtransmission mode.
 21. (canceled)